The principal objective of the Biostatistics Core will be to provide project investigators a centralized resource for biostatistics expertise. Statistical issues will be addressed at all levels of investigation: from the design of clinically based studies and laboratory experiments, to the maintenance of data quality; and from conclusions based on formal hypothesis testing, to important leads discovered by thorough data exploration. In support of this objective, the specific aims of the Core include: 1. Design: collaborate with project investigators in the design of laboratory experiments and clinical studies and the formulation of unambiguous hypotheses and hypothesis testing strategies. 2. Analysis: provide support for formal hypothesis tests in clinical and experimental data that ensure strong conclusions; statistical modeling and sensitivity analyses of prospective and retrospective studies; exploratory analyses that lead to further studies and experiments; and visual displays of data that clarify conclusions and uncover leads. 3. Data Quality Assurance: manage data and coordinate services with the Clinical Core A to ensure high quality, security and investigator accessibility for all clinical and experimental data. 4. Methods Research: Investigate new methodologies to directly address difficult data or design problems.